The present invention relates generally to an optical recording medium, an optical recording and/or reproducing method and an optical recording and/or reproducing system. More specifically, the invention relates to an optical recording medium which has a phase change type optical recording layer irradiated with light beams for reproducing and recording/reproducing information and which has a greatly improved recording density and an extended operating wavelength range by utilizing a superresolution function, and an optical recording and/or reproducing method and optical recording and/or reproducing system which is capable of providing a greatly improved recording density and an extended operating wavelength range by utilizing a superresolution function.
Optical recording media, which are irradiated with light beams for reproducing or recording/reproducing information, have been put to practical use, for various data files, such as voice data, image data and computer data, as recording devices having large capacity, rapid accessibility and medium portability, and the development thereof is expected in future. As an example of an optical recording medium, an optical disk will be described below.
As measures to enhance the density of optical disks, there are various approaches, such as the shortening of the wavelength of gas laser for an original disk cutting, the shortening of the wavelength of a semiconductor laser serving as an operating light source, the increase of the numerical aperture of an objective lens and the decrease of the thickness of an optical disk substrate. Moreover, in the case of recordable optical disks, there are various approaches, such as the mark length record and the land group record.
As effective density enhancing techniques other than these approaches, the xe2x80x9csuperresolution functionxe2x80x9d has been proposed and studied. This is a function which is obtained in a xe2x80x9csuperresolution filmxe2x80x9d. The xe2x80x9csuperresolution filmxe2x80x9d means a film having a characteristic that an optical response varies non-linearly in accordance with the intensity of irradiated light.
That is, generally used laser beams have a light-intensity distribution which is like a Gaussian distribution. The superresolution film has different response characteristics to the central portion (high intensity portion) and peripheral portion (low intensity portion) of such a light beam. By such a spatial difference in optical response, an optical mask or aperture is formed in the central or peripheral portion of an incident light spot to reduce an effective spot size, so that a high-density recording and/or reproducing can be carried out.
At first, such a superresolution function was proposed as a technique which is special to optical magnetic disks. That is, optical magnetic disks use a medium wherein a magnetic film having the superresolution function is switched-connected or magnetostatic-connected to a recording layer or a reproducing layer. Then, during irradiation with regenerative light, the temperature of the film is raised to utilize the exchange force or magnetostatic force between layers, so that an optical mask or optical aperture to a part of a regenerative spot is formed in a superresolution film.
Thereafter, a proposal for using a film material, which has a non-linearly varying optical response, without using magnetic functions, was made with respect to a read only memory disk. It was found that this proposal was applicable to all types of optical disks, such as optical recording ROM media, optical recording phase-change media and dye type recordable media, in addition to optical magnetic recording media.
Such superresolution reproducing methods and superresolution reproducing films capable of being applied to various optical disks are divided broadly into a heat mode system and a photon mode system. As disclosed in, e.g., ISOM""98-Technical Digiest (P126), the former system is designed to irradiate a superresolution film with regenerative light to heat the superresolution to cause a phase transition, such as melting, in the superresolution film to change the transmittance thereof. In this system, the response time up to the formation of an optical aperture or mask is relatively long. As disclosed in, e.g., ISOM ""98-Technical Digiest (p128), the latter photon mode system is designed to irradiate a superresolution film with generative light to cause the electron transition in the superresolution film to change the light transmittance by the absorption saturated phenomenon. The photon mode system is characterized in that the response time up to the formation of an optical aperture or mask is relatively short.
However, conventional optical recording media having superresolution films are limited to those having a monolayer superresolution film. However, in the case of the monolayer, there is a problem in that it is difficult to reduce the size of the optical aperture and to ensure a practical operating wavelength margin.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide an optical recording medium, an optical recording and/or reproducing method and an optical recording and/or reproducing system, wherein it is possible to greatly reduce the size of an optical aperture and to provide a higher density.
It is another aspect of the present invention to provide an optical recording medium, an optical recording and/or reproducing method and an optical recording and/or reproducing system, which can easily ensure a practical operating wavelength margin.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, an optical recording medium comprises a superresolution film which has a light transmittance varying in accordance with the intensity of incident light and which has a superresolution function for optically masking part of incident light to form an optical aperture having a smaller size than a spot size of incident light, the superresolution film including at least two kinds of superresolution materials having different response times until the superresolution function occurs after being irradiated with light.
With the above described construction, it is possible to easily and surely reduce the light spot size to greatly enhance the recording density.
If the superresolution film comprises at least two kinds of stacked superresolution films having different response times until the superresolution function occurs after being irradiated with light, it is possible to easily and surely reduce the light spot size via only a portion in common between the apertures of the two kinds of superresolution films, so that it is possible to greatly enhance the recording density.
Moreover, if the apertures formed in the at least two kinds of superresolution films when being irradiated with a light beam for writing or reading data partially overlap with each other, it is possible to easily and surely reduce the light spot size via only a portion in common between the apertures of the two kinds of superresolution films, so that it is possible to greatly enhance the recording density.
According to another aspect of the present invention, an optical recording medium comprises a superresolution film which has a light transmittance varying in accordance with the intensity of incident light and which has a superresolution function for optically masking part of incident light to form an optical aperture having a smaller size than a spot size of incident light, the superresolution film including at least two kinds of superresolution materials having different operating wavelengths causing the superresolution function.
With the above described construction, it is possible to greatly extend the operating wavelength range.
If the superresolution film comprises at least two kinds of stacked superresolution films having different operating wavelengths causing the superresolution function, it is possible to surely, easily and greatly extend the operating wavelength range.
In addition, if at least one kind of the at least two kinds of superresolution films is a superresolution film causing the superresolution function on the basis of electron transition, it is possible to easily select the response speed and operating wavelength by using a superresolution film of a photon mode system.
Moreover, if at least one kind of the at least two kinds of superresolution films is a superresolution film causing the superresolution function on the basis of temperature rise, it is possible to easily select the response speed and operating wavelength by using a superresolution film of a heat mode system.
According to another aspect of the present invention, an optical reproducing method comprises the steps of: preparing at least two kinds of superresolution films, each of which has a light transmittance varying in accordance with the intensity of incident light and each of which has a superresolution function for optically masking part of incident light to form an optical aperture having a smaller size than a spot size of incident light, the at least two kinds of superresolution films having different response times until the superresolution function occurs after being irradiated with light; irradiating the at least two kinds of superresolution films with a light beam for reading data so that the apertures formed in the at least two kinds of superresolution films partially overlap with each other, to irradiate an optical recording face of an optical recording medium with the optical beam via the optical apertures partially overlapping with each other; and detecting reflection of the light beam, with which the optical recording face is irradiated, to read data.
With the above described construction, it is possible to easily and surely reduce the light spot size to greatly enhance the recording density.
According to another aspect of the present invention, an optical reproducing method comprises the steps of: preparing at least two kinds of superresolution films, each of which has a light transmittance varying in accordance with the intensity of incident light and each of which has a superresolution function for optically masking part of incident light to form an optical aperture having a smaller size than a spot size of incident light, the at least two kinds of superresolution films having different operating wavelengths causing the superresolution function; irradiating the at least two kinds of superresolution films with a light beam for reading data to irradiate an optical recording face of an optical recording medium with the optical beam via the optical apertures; and detecting reflection of the light beam, with which the optical recording face is irradiated, to read data.
With the above described construction, it is possible to greatly extend the operating wavelength range.
According to a further aspect of the present invention, an optical reproducing system comprises: light irradiating means for irradiating at least two kinds of superresolution films, each of which has a light transmittance varying in accordance with the intensity of incident light and each of which has a superresolution function for optically masking part of incident light to form an optical aperture having a smaller size than a spot size of incident light, the at least two kinds of superresolution films having different response times until the superresolution function occurs after being irradiated with light, with a light beam for reading data so that the apertures formed in the at least two kinds of superresolution films partially overlap with each other, to irradiate an optical recording face of an optical recording medium with the optical beam via the optical apertures partially overlapping with each other; and data reproducing means for detecting reflection of the light beam, with which the optical recording face is irradiated by the light irradiating means, to read data.
With the above described construction, it is possible to easily and surely reduce the light spot size to greatly enhance the recording density.
According to a still further aspect of the present invention, an optical reproducing system comprises: light irradiating means for irradiating at least two kinds of superresolution films, each of which has a light transmittance varying in accordance with the intensity of incident light and each of which has a superresolution function for optically masking part of incident light to form an optical aperture having a smaller size than a spot size of incident light, the at least two kinds of superresolution films having different operating wavelengths causing the superresolution function, with a light beam for writing or reading data to irradiate an optical recording face of an optical recording medium with the optical beam via the optical apertures; and data reproducing means for detecting reflection of the light beam, with which the optical recording face is irradiated by the light irradiating means, to read data.
With the above described construction, it is possible to greatly extend the operating wavelength range.
According to the present invention, the spot size of a light beam for reproducing or recording information can be effectively reduced by stacking a plurality of superresolution films having different response times to irradiation with light. As a result, it is possible to improve spatial resolution and to realize a higher density optical recording.
In addition, according to the present invention, the wavelength margin of a light beam for reproducing or recording information can be extended by stacking a plurality of superresolution films having different operating wavelengths. That is, it is not required to strictly manage the wavelength of laser light which is a light source, so that it is possible to simplify the recording and/or reproducing system.
As described in detail above, according to the present invention, it is possible to realize a higher density optical recording with a simple construction to provide great industrial merits.